Assessing accurately the current state of the global
environment and increasing our predictive capabilities to aid in
anticipating how this environment may evolve are enduring
challenges to science. The U.S. Global Change Research Program
(USGCRP) seeks to advance scientific understanding of the global
environment, assist federal agencies in their missions, and provide
reliable information for decision making. The scientific and societal
motivations of the program remain compelling, and it should be
aggressively pursued.

Future development of the USGCRP should be based on a set of
guiding principles:

Science is the fundamental basis
for the USGCRP and its component projects, and that fundamental
basis is scientifically sound.

The balance of activities within the program
must reflect evolving scientific priorities.

In addition to observational systems and data streams
implemented as explicit components of the USGCRP, the program
should make use of existing observational systems and data
products implemented in support of related environmental
monitoring and earth science programs (e.g., the ground-based and
satellite observations that support operational weather
forecasting).

The USGCRP must utilize advancing technology in
addressing these evolving priorities.

An open and accessible program will encourage
broad participation by the government, academic, and private
sectors.

Success in attacking the long-term scientific challenges of the
USGCRP requires an adequate and stable level of
funding that promotes management efficiencies and
encourages rational resource allocation.

Successful implementation of the USGCRP and the realization of its
benefits require informed leadership and
collaboration among the government, academic, and private
sectors.

The USGCRP, furthermore, must be implemented as an
integrated program of observations, process
research, modeling, prediction, information management, and
assessment. In order to achieve this, enhanced collaboration
and cooperation are required among the scientific
community, the Congress, federal agencies, and the Executive Office
of the President to ensure that all elements of the program are
considered in the context of the integrated program as a whole.

The program should focus on priority issues in four mature
areas of Earth system science that are of great scientific and practical
importance. Each area will require the contribution of a variety of
traditional Earth science disciplines:

Seasonal to interannual climate
prediction: Improve prediction skills related to El Niñ o
and expand predictive skills beyond the tropics to the extent
possible; enhance understanding of land-atmosphere interactions;
and establish an international research prototype prediction
capability to garner multinational support and to provide benefits
to participating countries where usable predictive skill has been
demonstrated.

Atmospheric chemistry: Enhance research and
scientific assessment on tropospheric chemistry, including
tropospheric ozone and its precursors; characterize global
distributions of aerosols; monitor biogenic gases especially over
continental areas; and continue monitoring and scientific assessment
of ozone in the stratosphere, including links to climate.

Ecosystems: Improve documentation,
assessment, and understanding of the global carbon cycle; investigate
the relationships among vegetation, climate, and land use; study the
role of managed and natural ecosystems in the exchange of water,
carbon dioxide, and biogenic gases; and provide for the inclusion of
surface atmosphere processes and ecosystem dynamics in integrative
models and scientific assessments.

Decadal to centennial climate: document,
investigate, and assess changes in forcing factors that influence
climate; incorporate ocean, land, atmosphere, and ice processes and
feedbacks in coupled models; document change through long-term
monitoring and assessment of primary climate system
characteristics; and investigate economic, technological, and
demographic trends that affect the ability of natural and human
systems to respond to climate variability and
change.

These areas are at different stages of maturity. They have
different levels of access to existing remotely sensed data, and each
area can make unique contributions to the study of global change. In
all these areas, linkages among the physical, natural, and social
sciences should be enhanced, and effective U.S. participation in
international global change research programs should be
encouraged.

Observations of the Earth system play a key role in the USGCRP,
and the program requires an integrated observational strategy based
on scientific needs, the development and implementation of
observing systems appropriate to those needs, scientific guidance,
and the application of technological capabilities as appropriate.
NASA's Earth Observing System (EOS) should reflect that integrated
strategy.

Based on a series of reviews, the program has evolved from its
original plans to a reshaped program that is more responsive to the
science, more resilient, and more open to the introduction of new
technology. There has been a shift from a fixed series of large-
vehicle missions to a mixed fleet exploiting small to medium class
spacecraft. However, any further structural changes to the near-
term EOS missions would cause severe program dislocations. Further
budgetary reductions or imposed constraints on technical options
could require the elimination of key sensors, slips in schedule, loss of
data continuity, and the elimination of advanced technology
development that could enhance future research and lower costs.

However, continued evolution is essential. NASA, in concert
with the USGCRP community, should consider carefully the
observational strategy appropriate for the post-2004 era to ensure
that the EOS strategy remains technologically current and
scientifically relevant. In the meantime, as a result of technological
advances, scientific insights, and programmatic evolution, NASA
should move to rebalance the EOS program across space assets, in
situ measurements, modeling and process studies, and the data and
information management system through a set of feasible and cost-
effective actions.

Maintain a science-driven approach to
observational and information management technology.

Focus the tropospheric component of Chem-1 on the global
distribution of ozone and its precursors.

Implement a future framework for MTPE that incorporates
advanced instrumentation and vehicle technologies, such as small
satellites and remotely piloted vehicles (RPVs), as an integral
component of the program, including planning for EOS missions
beyond the first group of platforms. Incorporate scientific needs into
interagency and international planning for satellite convergence.

Streamline current the EOSDIS plans for data downlink and Level-
0 processing.

Reconfigure EOSDIS to transfer responsibility for product
generation, publication, and user services to a competitively selected
federation of partners in government, academia, and the private
sector.

The proposed rebalancing of the programs would offer the
potential for significant economies, (e.g., by focusing and simplifying
the tropospheric component of the Chem-1 mission on ozone and its
precursors, by streamlining the data downlink and initial processing
of EOSDIS, and by employing a federation of partners in EOSDIS for
product generation). The latter two potentially contribute the
greatest savings, and the last offers significant new opportunities to
research and private sector communities. To ensure scientific
success, however, it will be necessary to direct the resources toward
(1) expanding in situ observations, process studies, and large-scale
modeling; and (2) developing advanced technology to reduce the
costs of second- and third-generation missions and to open new
scientific opportunities. With integrated, science-driven, and
balanced scientific and observational elements, the USGCRP and
NASA's MTPE/EOS program can continue to contribute importantly to
ensuring our national welfare in a changing global environment.